Identification, enzymatic spoilage characterization and proteolytic activity quantification of Pseudomonas spp. isolated from different foods

• A large diversity of Pseudomonas species was found over the different food matrices.
• All isolates were able to produce enzymes and/or pigments that can affect foods.
• A perfect match was found between proteolytic activity and presence of aprX gene.

Sixty-six putative Pseudomonas strains isolated from different food matrices (ready-to-eat vegetables, meat, milk and dairy products) were examined for their phenotypic features and enzymatic spoilage activities. Their genotype was studied by BOX-PCR, Pseudomonas specific 16S PCR, aprX and housekeeping genes sequencing (16S rRNA gene, gyrB and rpoB). The majority of the isolates are very versatile as shown by their wide ranges in growth temperature (4–45 °C), pigment production and production of enzymes. The BOX-PCR clustering showed a high genetic diversity among the isolates and phylogenetic analysis of the rpoB gene allowed a first putative identification at the species level. Thirteen isolates were provisionally classified as Pseudomonas gessardii-like, but probably belong to a yet unknown Pseudomonas species in the Pseudomonas fluorescens group.Protease-activity was qualitatively and quantitatively verified. A large variation in proteolytic activity measured in UHT-milk was observed amongst the protease positive isolates. Several isolates provisionally classified as P. gessardii-like showed the highest activities. An aprX gene based phylogenetic dendrogram showed five different groups and two sub-groups, for which a correlation with the matrix of origin could be demonstrated. An insertion of 15 bp was observed in the aprX gene sequences of isolates of mainly dairy origin.